Abrasive product



Patented July 13, 1943 ABRASIVE PRODUCT Norman r. Roble, Lewiston, N.1., asslgllol' to The Carborundum Company, Niagara Falls, N. 1., acorporation of- Delaware No Drawing. Original application sum 17, 1940,Sel'lll No. 353,065. Divided and this appllcation April 29, 1942, SerialNo. 411,019

Claims. This invention relates to abrasive products such as abrasivepaper and cloth, polishing set- Y up wheels and grinding wheels, and tomethods of manufacturing the same. More specifically, the invention isconcerned with abrasive articles wherein there is employed as a bindereither in whole or in part, a composition which includes a salt of anethenoid resin. The invention is particularly well-adaptedto theproduction of coated abrasive products such as abrasive paper and clothand set-up wheels.

' This application is a division of my copending application Serial No.353,065, filed August 1'7, 1940.

An object of the invention is the provision of improved abrasivearticles including an improved binder. Another object of the inventionis to provide a coatedabrasive article containing a binder whichincludes as an essential ingredient a synthetic gum which can be takenup in water and consequently can be substituted for glue'in the ordinarysandpaper machinery. Another object-of the invention is the provision ofimproved 'binders for coated abrasives comprising a salt of an ethenoidresin. Other objects will appear from a consideration of the descriptionof the invention as hereinafter set forth.

The ethenoid resins employed inmy invention are those formed by thepolymerization of compounds containing adouble-bonded carbon atom,

there-being always included in the polymer a substantial proportion of acompound which conwith water-soluble inorganic bases or amines, arewater-soluble. In one case the binders comprise the salts of polymers ofan acrylic acid.

In the second case, esters are formed by reacting only a part of thecarboxyl groups appearing in the monomer with polyvinyl alcohol andneutralizing additional carboxyl groups with alkali to form salts.Thethird class includes the salts of heteropolymers in which the doublebond of an ethenoid linkage is opened up to join a vinylor acryliccompound containing an acid group and provide a polymer containingorganic acid groups in the chain, these latter groups being neutralizedwith the alkali to form the salt.

Specific compounds of the first class, the salts of which have beenfound to be suitable in carrying out my invention include polyacrylicacid and polyalpha-methacrylic acid. As is known, compounds of thisclass can be polymerized by subjecting the monomeric compounds tosuitable treatment such as by exposure to ,ultra violet light or heatingor by the employment of a-suitable catalyst such as oxidizing agentslike hygroups which are neutralized. In describing and claiming suchesters, I have chosen to refer to 1 such compounds, in which only partof the acid tains a neutralized organic acid group. Ex-

amples of ethenoid resins which are capable of forming salts byneutralization with alkalis and are therefore useful in my invention arethe polyacrylic acids; heteropolymers of vinyl or acrylic compounds witholefinic acids, and partial vinyl esters of polybasic acids whichcontain free acid groups.

Alkalis which may be employed to form, with the acid-containing ethenoidresins, the salts which are used in my invention include the inorganicbases such as sodium, potassium and ammonia, and organic ba'ses such asdior triethenol amine, the amyl amines and pyridine.

It will thus be seen that there are three specific classes of ethenoidresins which meet the groups in the polybasic acid areesterified, aspartial polyvinyl esters." For example, a polyvinyl ester of a monobasicacid, such as polyvinyl'acetate, may be subjected to the action of apolybasic acid so as to replace some or all of the acetic acid groupswith polybasic acid groups.

Sufilcient polybasic acid is used to give the final gum enough free oruncombined carboirylic groups to make it reactivewith alkaline to formsalts. Suitable polybasic acids for this purpose are citric, tartaric,maleic, oxalic, succinic, malic and phthalic acids. In plac of apolycarboxylic acid, I may use a polybasic acid in which one or more ofthe acid-groups are the sulphonic acid (BOaH) group. The productsobtained have requirements of my improved binder. A commoncharacteristic of the ethenoid resins which'are neutralized to form asalt is the presence of a widely varying properties depending upon manyfactors such as the molecular weight of the original polyvinyl acetate,the proportion and type ature, solvents and catalysts used in thereaction.

' I may also employ the salts of copolymers and of polybasic acid used,andthe time, temperheteropolymers of these partial polyvinyl esters ofpolybasic acids. These may beproduced by partial reaction, by partialhydrolysis or by using -hyde to form an acetal.

copolymers and heteropolymers or their components as the raw materialsfor the production of copolymers and heteropolymers of partial polyvinylesters of polybasic acids. Still another method of preparing these saltsof partial esters is to esterify polyvinyl alcohol with polybasic acids,their anhydrides or their chlorides and pound containing a vinyl groupwithan olefine carboxylic acid or a compound capable of form- 'ing suchan acid. Specific materials containing the vinyl group are styrene orvinyl benzene, and vinyl and acrylic acid esters such as vinyl acetateor chloride and methyl acrylate or methacrylate. Alternatively, theheteropolymers may be hydrolyzed to form heteropolymers of vinyl alcoholwith the acids, or the heteropolymer may be preliminaril hydrolyzed andreacted with an aide- Suitable oleflne acids and derivatives includemaleic, fumaric, crotonic, itaconic and citraconic acids and theanhydrides, chlorides, nitriles and other derivatives capable ofconversion to the corresponding acids.

The formation of the polymer may be induced by any of the conventionalmethods employed in polymerization as by heating, exposure to ultraviolet light and the addition of suitable catalysts.

In making abrasive coated products, a coating of liquid adhesive isapplied to the backing material, abrasive grains are distributed overthe adhesive-coated surface, and the thus-coated article is treated tosolidify the liquid adhesive. A second-oating of adhesive, usuallycalled a sizing" coat, is commonly applied after the grains have beenattached by the first or making coat of adhesive to provide additionalbinder for the grains. This sizing coat must also be hardened.

In preparing the liquid adhesives used in my invention I first make upapolymer of the acidor acid-containing compound, preferably one having ahigh molecular weight because such resins are tougher and make betterbinders, and

I then dissolve the polymer in a solution of an alkali. While suflicientalkali to neutralize all of the acid may be used, I have found thatsolutions may be. prepared by 'using less alkali than is needed tocompletely neutralize the acid and that both the liquid adhesives andthe solidified binders thus prepared are eminently satisfactory for' usein the invention.

. I have also found that the invention can be carried out bystarting'with a polymerized derivative of an acid such as a nitrile ora, chloride instead of the acid itself. In this modification of.

my invention the binder comprises in part a salt of the correspondingpolyacrylic acid and in part the polymerized derivative. Fm'thermore byincluding some ammonia in the water used to dissolve the resins thecorresponding polyamides may be formed, thus further modifying theprop-' erties of the hardened binder, the characteristics of whichdepend upon the composition of the solidified binder, obtained after thehardening treatment.

The adhesive coating and the abrasive grains may be applied by any ofthe methods used in the manufacture of coated abrasive articles. For

example the adhesive may be applied by passing a moving web between apair of rolls one of which is rotated while partially immersed inc. vatof the liquid. Alternatively the adhesive may be brushed or sprayed ontothe backiDB.

The hardening treatment which'is used to solidify and set up the liquidadhesive comprises as an essential step the removal of water. This stepmay be carried out in the manner commonly used in the manufacture ofvglue bonded sandpaper where the coated web is'festooned and hung indrying chambers which causes evaporation of the water under controlledconditions. 1

While I have found that articles bonded with these salts of polyacids orpolymers containing acid groups are superior for many purposes, myinvention includes other modifications or embodiments which constituteadditional improvements over theprior art for some purposes. In thismodification of the invention the salts of my invention are not used toform the entire binder for the abrasive'grains but rather they aremodified by the inclusion of other bonds which are compatible with themin both the liquid and the final solid conditions.

I have found that other kinds of binders which have been previously usedin the manufacture of abrasive articles may be substituted for a part ofthe salts which form the principal feature of the invention. Examples ofsuch binders are cellulose derivatives, suchas cellulose esters andethers, and heat hardenable resins a'sexemplified' byphenol-formaldehyde condensation products.

The use of combinations of the salts with these other binders has anumber'of advantages. For example the salts of polyacrylic acids havebeen found to be excellent dispersing agents for promoting andstabilizing aqueous dispersions of solutions of esters in organicsolvents. Where they 'are so used the products serve the dual functionof acting as a dispersing agent for the esters in the liquid state andplacticizers or modifiers forthe esters when they are solidified and arefunctioning as a binder for the abrasive grains.

Cellulose esters such as cellulose nitrate or acetate have previouslybeen suggested as binders for coated abrasives but so far as applicantis aware they have not been used because it, has been necessary toliquefy them by dissolving in organic'solvents. These solvents areexpensive, explosive, and otherwise undesirable. By dispersing theesters in water with the aid of salt of my invention as the dispersingagent it is unnecessary to use much solvent because the esters can bemade dispersible by takin them up in a small amount of solvent and thenliquefied to the desired viscosity with water.

As indicated the salts may also be blended with other types of resins toassist in liquefying the resins and to modify their properties when theyare in the solid condition and functioning as the binder for theabrasive grains. Phenol-formaldesalts which are relatively flexible andthese classes of resins may be advantageously employed in pconjunctionwith the more inflexible resins as exemplified by the hardened phenolicresins.

My invention has a number of advantages over the articles of the priorart. Products made in accordance with the invention have been found tobe superior to glue-bonded sandpaper for many purposes. As has beenpointed out they are an improvement over articles "employing phenolicresins as a binder because they may be made more flexible. Furthermorethe binders may be liquefied with water and they therefore can beapplied on machinery commonly used in making sandpaper with glue binder.The hazards and expenses coinciden'tto the use of organic solvents areeliminated. They also make it possible to produce coated abrasivearticles which are particularly well suited to the treatment ofdiflerent classes of materials. Heretofore it has been customary to useglue-bonded products on all classes of work and it has not been possibleto provide special bonds for special purposes as is coinmonly done withabrasive wheels. By utilizing 1. an abrasive article comprising abrasivegrains and a-binder therefor comprising the neutralization product of analkali with a partial polyvinyl ester of a polybasicacid.

2. An. abrasive article comprising abrasive grains and a binder thereforcomprising the neutralization product of an alkali with a partialpolyvinyl ester ofa dibasic acid.

3. An abrasive article comprising abrasive grains and a binder thereforcomprising the neutralization product of an .alkali with a partialpolyvinyl ester of tartaric acid;

4. An abrasive article comprising abrasive grains and a binder thereforcomprising a 'neutralization product of an alkali with a partialpolyvinyl ester of oxalic acid.

5. 'An abrasive article comprising abrasive grains and a binder thereforcomprising the neutralization product of an alkali with a partialpolyvinyl ester of citric acid. I

' NORMAN. P. ROBIE.

